With the popularization of the Internet, private Local Area Networks (LAN) in houses and buildings are being set up using wireless communication. The wireless LAN conforms to a physical layer and a MAC layer specified in the IEEE 802.11, and realizes multiplexing of multi-users by access control based on the Carrier Sense Multiple Access with Collision Avoidance (CMSA/CA),method (for example, see Non-patent literatures 1 and 2).
In such a conventional wireless LAN system, multi-point wireless connection of maximum 54 Mbps is realized through the physical layer and the MAC layer specified in the IEEE 802.11. However, to realize the wireless connection of 54 Mbps, it is necessary that the transmission distance is short, and that there are minimum wireless deterioration factors. In reality, the transmission distance can be long, and there are wireless deterioration factors, such as reflection on the wall.
To handle this problem, Non-patent Literature 1 and 2 disclose an automatic adjusting function with a plurality of different transmission rates. In other words, when the transmission distance is long, or when there is a wireless deterioration factor, the transmission rate is reduced to 48 (Mbps), 36, 24, 16, . . . , to secure the wireless connection.
Furthermore, the conventional wireless LAN discloses in the Non-patent literature 1 and 2, that there is a handover function for searching a wireless LAN base station (hereinafter, “AP”) at the destination and reconnecting the terminal and the AP, in the case of moving a wireless terminal.
Non-patent literature 1: IEEE 802.11 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications 1999 Edition
Non-patent literature 2: Hideaki MATSUE and Masahiro MORIKURA, “802.11 High-speed Wireless LAN Textbook”, IDC Japan, Mar. 29, 2003, P. 49 to 51, and P. 84
In the conventional techniques, it is attempted to handle the long distance communication and wireless deterioration factors by reducing the transmission rate. Hence, there is a problem in that high-speed transmission cannot be realized in long distance communication, and under bad wireless conditions.
Furthermore, in the conventional wireless LAN, the handover function is provided, but can be used only for semi-fixed use, such as a Notebook PC used in an office is also used in a meeting room. If the wireless LAN is used while moving at a high speed, the handover time increases, thereby making a data interruption time long.
In view of the above problems, it is an object of the present invention to provide a wireless LAN system, a diversity device, and a wireless LAN terminal that can realize high-speed transmission and ensure a low error rate, even under bad wireless conditions and in long distance communication.
It is another object of the present invention to provide a wireless LAN system, a diversity device, and a wireless LAN terminal that can reduce the time of temporary disconnection at the time of handover, when the wireless LAN terminal moves between the wireless LAN base stations.